In 1983 Thornton commissioned Michael Heizer, a pioneering figure in the American Land Art movement known for monumental earthworks like Double Negative, to conceive a site nspecific work. Originally he wanted to do eight mounds, budget constraints reduced that to five. Workers used bulldozers and earth movers to sculpt slopes and edges. The scale was huge. Together the mounds were estimated to weigh more than a quarter of a million tons. Once the mounds were shaped they were covered with mats of “excelsior” which are shredded aspen fiber woven into a plastic netting that was meant to hold the soil in place until grass could take root. Then workers used trucks to blow shredded straw, grass seed, and fertilizer over the site. The area around the mounds, too, was graded, fertilized, and reseeded.

It was completed, dedicated, and deeded to the neighboring state park, vastly increasing its size. It took another two years for the Department of Conservation to complete a trails, signage, and observation decks. For a few years after, there were issues with Buffalo Rock Shooters Supply and its successor, Buffalo Pit and Range, having a gun range aimed south at the previously empty mining site. No one was hurt, but there were multiple incidents of vehicles and trees being hit by bullets. It closed areas of the park down in 1988 and 1990 while legal battles ensued. The gun range still operates today, and I can confirm that I did not hear or see any gunfire, so I assume developments over the past 30 years have been positive.

Effigy Tumuli was hailed as a bold fusion of mine reclamation and land art when it opened. A 1985 Christian Science Monitor profile described it as “grand sculpture in the tradition of Mt. Rushmore and the Egyptian pyramids,” while also praising its ecological renewal. ARTnews called it “a creative solution to the environmental problems of a once ruined and poisonous site.” Alice Thorson, the magazine’s critic, looked north across the valley to the barren gray hills that today house the Buffalo Pit and Range: “As yet unreclaimed cratered mine sites, dotted with sinister-looking pools of contaminated water, offer a sober ‘before’ picture. It is this contrast, coupled with the evocative associations of the tumuli, that ultimately endows Heizer’s piece with power and romance. . . . At once monument, playground and art object, Effigy Tumuli may well turn out to be one of the country’s most successful public sculptures,” she concluded.

Locally, however, opinions were mixed: the scale and maintenance challenges meant the forms were rarely distinct from the ground, and the site never achieved the tourism draw intended. But most local citizens, says Thornton, didn’t quite get it. “Some thought it was amusing,” he says. “Some thought it was a waste of time and money. Others were intrigued by it.” Some criticism stemmed from the fact that it’s hard to tell from the ground what the mounds are supposed to represent. Heizer has said this was part of his intent: “It requires a chronological development of perception. It’s a diffracted gestalt.”